Method of cladding of metal products

ABSTRACT

In a method of cladding metal products, the workpiece being clad is placed on a support and subjected to cladding by the explosive-welding technique. In the capacity of a support for accommodating the workpiece being clad, use is made of a &#39;&#39;&#39;&#39;pad&#39;&#39;&#39;&#39; of metallic shot, a direct physical contact between the workpiece and the pad being established.

United States Patent [191 Apalikov et a1.

1 Mar. 4, I975 1 METHOD OF CLADDING OF METAL PRODUCTS [76] Inventors: Jury lgnatievich Apalikov, prospekt Lenin-a, 96, kv. 44; Leonid Leonidovich Bankovsky, ulitsa lsakova, 141, kv. 55, both of Barnaul; Alexandr Shmulievich Gelman, 3-ya Tverskaya-Yamskaya, 42/8, kv. 46. Moscow; Jury Alexeevich Konon, ulitsa Novaya, 6, kv. 4l, Barnaul; Leonid Borisovich Pervukhin, ulitsa Jurina, l 16, kv. 40, Barnaul; Boris Davydovich Tsemakhovich, prospekt Lenina, 69-, kv. 41, Barnaul; Grigory Abramovich Bronovsky, ulitsa 7-ya Sovetskaya, 7, kv. 6; Vitaly Moiseevich Poretskin, prospekt Zanevsky, 28, kv. 201, both of Leningrad; Petr Pavlovich Tokarev, ulitsa Burjuzova, 8, kv. 47,

Odintsovo, Moskovskoi oblasti, all

of U.S.S.R.; Boris Agafonovich Barinov, deceased, late of prospekt Lenina, 63a, kv. 6, Barnaul, U.S.S.R. by Raisa Alexeevna Alinina, administrator 22 Filed: Mar. 22, 1973 211 App]; No.: 344,028

[52] US. Cl. 29/470.1, 29/493 [51] Int. Cl. B23k 21/00 [58] Field of Search 29/4931, 470.1, 421 E, 486,.

[56] References Cited UNITED STATES PATENTS 2,979,808 4/1961 Booth 29/493 X 3,220,105 11/1965 Gill, Jr. 29/493 X 3,434,197 3/1969 Davenport 29/470.1 3,474,520 10/1969 Takizawa et al 29/470.1 R26,858 4/1970 Chudzik 29/470.l

Primary E.\'aminerFrancis S. l-lusar Assistant E.\'aminer-Ronald .1. Shore Attorney, Agent, or Firm-Holman & Stern [57] ABSTRACT In a method of cladding metal products, the workpiece being clad is placed on a support and subjected to cladding by the explosive-welding technique. In the capacity of a support for accommodating the workpiece being clad, use is made of a pad" of metallic shot, a direct physical contact between the workpiece and the pad being established.

5 Claims, 4 Drawing Figures METHOD OF CLADDING OF METAL PRODUCTS BACKGROUND OF THE INVENTION The present invention relates generally to methods of cladding metal products by the explosive-welding technique.

The invention can find most utility when used for cladding metal products of intricate shape such as blades of hydroturbines, large in size (of the order of to m or most vital or critical metal items involving minimized residual strain.

It is common knowledge that there exist nowadays a number of methods for cladding metal products, wherein the latter are placed on a support and are clad by the explosive-welding technique.

In such a cladding practice substantial effect upon the quality of the weld joint obtained is exerted the support upon which the workpiece being clad is placed.

A number of specific requirements are imposed upon such support, the cardinal ones (especially in case of mass production schedule) being long service life accompanied by good absorbability of explosion shock waves and minimized residual strain of the workpiece.

Moreover, the support must possess versatility, i.e.,

be suitable for accommodating thereon workpieces of r a variety of shapes and sizes, as well as incompressibil- 'ity to ensure easy and accurate trimming of overhang margins of the sheet of cladding material; besides, the support must be hard and stiff enough to prevent the workpiece from being sunk thereinto.

In order to bring mechanization and automation into auxiliary jobs, especially in mass-production schedule, the support must hold the workpiece firmly enough to prevent its being thrown down therefrom.

Most broadly used heretofore are the following supports for accommodating workpieces subjected to cladding by the explosive-welding technique: ground-andsand, crushed stone or rubble, all-metal, rubber-andmetal or reinforced-concrete supports.

Each of the above-stated supports suffers from its particular disadvantages.

Thus, the explosive-welding process effected on ground-and-sand supports causes heavy residual strain of the workpieces, especially of large-size one (over 3 m long). Due to high yieldability of such supports the workpiece being clad is liable to sink thereinto for a considerable depth as compared to its thickness, which renders the extraction of the workpiece rather difficult and involves much labor to restore the support for further use.

Furthermore, when cladding thin workpieces (under 10 mm thick) there occurs lack of side fusion-due to overhang margins of the sheet of cladding material getting in touch with the support before their trimming, due to the effect of the explosion impact.

Crushed-stone or gravel supports behave during the explosive-welding process rather better than those mentioned above; however, they fail to be fully free from the disadvantages inherent in the latter.

As to all-metal supports, these suffer from low durability, since they are liable to destruct after but a few explosion processes besides, such supports render it impracticable to clad intricately shaped products (such as hydroturbine blades) due to extremely laborious operations involved in matching the profile of an all-metal support to accommodate such products thereon.

Furthermore, when cladding a product placed on an all-metal support, the product is liable to be thrown down from the support at the moment of explosion which results, especially in case of cladding in explosion chambers, results in damaging the product.

Somewhat better operational behavior is featured by rubber-and-metal supports which are made as a gang of metal sheets interleaved by rubber sheets. However, the top metal sheet is liable to loose shape after first explosion process, if it is rather thin; if it is of heavy thick ness, such a support acquires disadvantages inherent in all-metal ones.

Reinforced-concrete supports though suitable for cladding intricate-shaped products, are in fact discardable and, consequently, too expensive.

Besides, all-metal and reinforced-concrete supports for cladding heavy large-sized products thereon render some difficulties for transportation thereof.

SUMMARY OF THE INVENTION It is an object of the present invention to devise a method of cladding metal products which will provide such a support for accommodating the workpiece being clad that will possess long service life.

It is another object of the present invention to devise a method of cladding metal products which will provide such a support that will be reliable in operation and convenient in service.

It is one more essential object of the present invention to devise such a method of the character mentioned above that will be instrumental in attaining highquality weld joint.

In keeping with these and other objects in the proposed method of cladding metal products, wherein the workpiece is placed on a support and is subjected to cladding by the explosive-welding technique, according to the present invention as a support for accommodating the workpiece being clad thereon, use is made of a pad of metallic shot with which the workpiece is in a direct physical contact.

The method provides for high quality of the weld joint obtained due to a direct physical contact of the workpiece being clad with the metallic shot of the pad" which conduces to a reliable absorption of shock waves produced by explosion and to negligible residual strain of the workpiece.

Since metallic shot is practically incompressible, this makes it possible to obtain clear-cut trimming of the overhang margins of the sheet of cladding material and to keep the workpiece lying on the surface of the pad."

Good dispersity of such a support renders it highly durable, involves only inconsiderable restoring work, provides for good absorption of explosion impact and prevents the workpiece from being thrown down therefrom.

It is favorable for accomplishing these objects that the material of the shot have physico-mechanical properties substantially close to those of the workpiece being clad.

With the above requirement fully met, a more reliable absorption of shock waves produced by the explosion during a direct physical contact of the support with the workpiece being clad is attained which, in turn, contributes to a high-quality weld joint.

It is expedient that the pad of metal shot be accommodated in a container, wherein at least the top portion of one of the walls subject to maximum impact load at the moment of the explosive-welding process, is made of a pliable material and adapted for an unobstructed discharge of some amount of the shot from the container at the moment of explosion.

Due to such an embodiment of the support, the proposed method requires a minimum scope of restoring jobs and provides for high durability of the support.

When cladding process occurs in a medium under sub-zero temperature, the pad of metallic shot is expedient to be preheated to a temperature that allows the workpiece to have an above-zero temperature at the moment of explosive-welding. This makes possible the cladding process to occur at fairly high impact strength of the material of the workpiece being clad.

It is also favorable for cladding workpieces thinner than 40 mm that the pad of metallic shot be located in a container and submerged in a liquid.

This protects the bearing surface of the workpiece being clad from deformation and retains its trade appeal.

The pad of metallic shot is expedient to be embraced in an air-inflated tire to establish the support for accommodating the workpiece to be clad mostly in explosion chambers.

Thus, the method of cladding metal products, according to the invention makes provision for a support to accommodates the workpiece being clad thereon that possesses high durability, reliability in operation, convenience in service and due to which the proposed method is instrumental in obtaining high-quality weld joints.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more evident from a consideration of a number of illustrative embodiments thereof given in a disclosure that follow and shown in the accompanying drawings, wherein:

FIG. I is a schematic arrangement diagram of a cladding sheet carrying an explosive charge, and the workpiece being clad as placed on the support, according to the invention;

FIG. 2 is a schematic arrangement diagram of a cladding sheetcarrying an explosive charge, and the workpiece being clad as placed on the support which is made as a pad of metallic shot accommodated in a container, according to the invention;

FIG. 3 is a diagrammatic view of the workpiece being clad as placed on a pad of metallic shot which is accommodated in a container adapted for heating the shot, according to the invention; and

FIG. 4 shows the workpiece being clad as placed on a pad of metallic shot and embraced in an airinflated tire, according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Disclosed herein is a method of cladding metal products, wherein the workpiece is placed on a support and subjected to cladding by the explosive-welding technique.

According to the invention, as a support for accommodating a workpiece 1 (FIG. 1) to be clad, use is made of a pad 2 made of metallic shot with which the workpiece makes a direct physical contact.

A cladding metal sheet 3 is positioned with a gap h relative to the workpiece 1 being clad and is larger in size by the amount a of the overhang margins. A charge 4 of an explosive having an estimated height H islocated on the surface of the sheet 3.

The value h and the estimated height H of the charge are calculated by the way well known by those skilled in the art.

The charge 4 is initiated by means of a detonating fuse 5.

Cladding by the explosive-welding technique is performed by the parallel method in a conventional way and therefore is left beyond the scope of the present disclosure to describe in detail so as not to obscure the essentials of the invention.

At the moment the charge 4 is blasted by the detonating fuse 5, the cladding sheet 3 is impinged upon the workpiece 1 being clad with the result that a weld joint is thus obtained.

The explosive-welding process scatters only a minute quantity of the shot in a close proximity to the bearing surface of the workpiece being clad.

The majority of the metallic shot of the pad remains in place.

That portion of the shot which is located immediately underneath the workpiece being clad remains in its place due to the fact that it is practically incompressible.

The amount of scattered shot located close to the bearing surface of the workpiece being clad is negligible due to large specific gravity of the shot. Thus, the specificgravity of of bulk cast-iron pellets 3 mm in diameter equals 5.0 to 5.5 kgf/cm.

In order to restore such a support, viz, a pad of metallic shot upon explosion, it is quite enough replace the amount of shot scattered, whereupon the support is again ready for accommodating the workpiece being clad thereon.

Consequently, such a support turns to be a reusable one.

The support of the invention is a versatile one as it enables accommodation of workpieces of a diversity of shapes and practically unlimited size (in excess of 20 m thereon. It is quite evident that preparation of such a support for accommodating the workpiece being clad thereon to a small extent depends upon the workpiece configuration and is independent of the personal skill of the operator.

Due to the support made as a pad of metallic shot being practically incompressible and having good dispersity and large mass, as well as due to a uniform direct physical contact of the support with the workpiece being clad (over the entire bearing surface thereof), the latter is imparted minimum residual strain during the cladding process, i.e., it retains to the maximum degree its shape and therefore needs no further trueing nor retouching.

As it is commonly known, trueing of a workpiece after having been clad by the explosivewelding technique involves preliminary heat treatment ofv same due to the facts that it becomes brittle which results from a considerable peening of the workpiece upon sustaining explosion impact loads. However, heat treatment of clad workpieces is far from being always permissible and feasible, e.g., due to the formation of intermetallic compounds in the zone of the weld joint in the course of heat treatment.

Thus, the proposed method can be efficiently used for cladding those metal products upon which higher requirements are imposed so as to the retention of their trade appeal and which cannot be, for some reason or other, subjected to heat treatment.

A support made according to the invention is convenient and reliable in operation.

Incompressibility of such a support prevents the workpiece being clad from being sunk thereinto at the moment of explosion and thereby conduces to a clearcut trimming of the overhang margins of the cladding sheet which is a practical warranty of a 100 percent welding continuity.

The support of the invention being a dispersive one, a considerable portion of explosion impact is damped due to friction between individual pellets, and the workpiece is prevented from being thrown down from the support.

The method of the invention makes it possible to effect high-quality cladding of intricate-configuration workpieces. Due to good dispersity of such a support, metallic shot can be used to forcely fill the interior space of any configuration by means of shot blasters, trying to attain a direct physical contact of the support with the bearing surface of the workpiece, or the latter upon being placed on the support can be exposed to vibration for same purpose. Such a support for cladding workpieces of practically any size is transportable as it can be transferred to the place of explosion piecewise thanks to the dispersity of the pad of metallic shot.

According to the invention, the material of shot is to be selected proceeding from the requirement that it possesses physico-mechanical properties substantially resembling those of the material of the metal product being clad.

We have found that when the workpiece being clad is in a direct physical contact with the support made as a pad of metallic shot whose material by its physicomechanical properties is close to the material of the workpiece being clad, such a support behaves as it were an integrated mass having an acoustical resistance close to that of the workpiece being clad which contributes to more reliable absorption of shock waves arising during explosion, thereby enabling high-quality weld joint to be obtained.

For example, for cladding steel products it is expedient to use a pad composed of steel or cast-iron shot.

Such shot features good strength characteristics and retains its shape and size for a long period of time in the course of service life, thus rendering the support substantially durable.

Besides, steel or cast-iron shot is of high specific gravity (5.0-5.5 kgf/cm when in bulk) which is of importance for damping explosion impact and renders the support less yieldable. This, in turn, ensures high quality of the weld joint throughout the surface being clad.

According to the invention, the pad 2 (FIG. 2) made of metallic shot and carrying a workpiece 6 being clad (the blade ofa hydroturbine), is accommodated in a container 7, wherein a top portion 8 of at least one wall 9 sustaining maximum load at the moment of explosive-welding is made of a pliable material and adapted for an unobstructed discharge of some amount of shot from the container 7 at the moment of explo- We have found that when the pad of metallic shot is accommodated in a container the amount of shot scattered by explosion is substantially decreased which sharply reduces the scope of the support restoring jobs.

In order to make the container durable and reliable in operation and, consequently, the support as a whole, the top portion 8 of the wall 9 is made of a pliable material such as rubberized band or cord. The portion 8 is connected to the wall 9 by means of bolts 10 and is held vertical before explosion through threads 11 fixed to the end face of the workpiece 6 being clad.

At the moment of explosion the overhang margins a of the cladding sheet 3 get trimmed and, in turn, cut the threads 11. As a result, the portion 8 loses its verticality and folds outside the container 7. Thereby a free discharge of some amount of shot from the container is ensured which, in turn, relieves the container itself from the effect of forces resulting from impact loads imposed upon the support during explosive-welding.

According to the invention, when cladding of metal products occurs in a medium under subzero temperatures, the pad of metallic shot is to be preheated to a temperature enabling the workpiece to acquire above-zero temperature by the moment of explosion welding.

It is common knowledge that impact strength of the majority of metals and alloys is liable to decrease severely at subzero temperatures. Thus, impact load developed during cladding by the explosive-welding technique results in considerable defects of the workpiece being clad or in a complete destruction thereof.

Heating of the pad of metallic shot carrying the metal workpiece being clad, due to high thermal conduction of metals, enables the workpiece being clad to have above-zero temperature by the moment of explosion welding even in case of subzero temperatures of the ambient medium.

This fact is of special importance when cladding large-sized (15-20 m workpieces under field conditions at subzero ambient temperatures.

The *pad" of metallic shot can be heated by any of the conventional method suitable for the purpose.

In the herein-considered specific embodiment of the invention the pad 2 (FIG. 3) is heated by firing any combustible in spaces 12 which are essentially pipe lengths 13 located inside the container 7 throughout the length thereof at a depth large enough to preclude their deformation during explosion, and spaced equidistantly across the container width.

In case of cladding metal products thinner than 40 mm the pad of metallic shot located in a container is expedient to be immersed in a liquid.

Experiments have shown that when cladding such workpieces on a support made as the pad of metallic shot, the workpiece due to its low specific mass is imparted a considerable velocity during explosion welding with the result that indents or dints appear on the bearing surface thereof from pellets.

The specific mass of a workpiece implies the mass per unit area of the workpiece being clad. Thus, the thinner the workpiece being clad the higher the velocity it acquires during the welding process and the deeper the indents left by the pellets on its bearing surface, the depth of the indents in some cases reaching 1.5 mm.

It is obviously that such indents on the bearing surface of the vital or critical parts, as well as on that of the products upon the trade appeal of which'especially strict requirements are imposed, are absolutely impermissible.

Filling of the container accommodating the pad, with a liquid retains a direct physical contact of the shot with the workpiece being clad, the area of contact of both increasing to 100 percent (making allowance for the contact of the workpiece also with the liquid filling all the interpellet space).

Any liquid being incompressible, it takes up a considerable portion of explosion impact, thereby reducing the specific contact pressure exerted by the shot upon the workpiece which precludes the formation of the shot indents on the workpiece bearing surface and diminishes the residual strain of the latter.

The method of the invention is instrumental in cladding workpieces thinner than l mm with the high quality of the weld joint obtained over the entire surface being clad.

It is quite obvious that when filling the container with a liquid one should prevent the latter from getting onto the workpiece surface being clad. if otherwise, lack of penetration in the weld joint might occur.

Water can be used as a filling liquid.

However, from the viewpoint of durability of the support and provision of a direct physical contact of the shot with the workpiece bearing surface during a repeated use of the support, the liquid must be selected proceeding from its being non-corrosive with respect to the metallic shot.

According to the invention, the pad of metallic I shot is embraced in an air-inflated tire 14 (FIG. 4).

We have established that such a support, due to elastic strain of the air-inflated "tire 14 and its top portion 15 being relieved at the moment of explosion due to partial discharge of the shot therefrom, acquires high durability.

Such a support possesses long service life, is reliable in operation, simple in service, inexpensive since it allows the utilization of used-up tires. However, in this case the area of the workpiece being clad is restricted to the area b of the free surface of the air-inflated tyre The use of such a support is especially favorable in explosion chambers.

What we claim is:

1. In a method of cladding metal products, wherein the workpiece being clad is placed on a support and subjected to cladding by the explosive-welding technique, the improvement which comprises the steps of providing a pad" of metallic shot with which the workpiece being clad makes a direct physical contact so as to be the support for accommodating the workpiece; and selecting the material of the metallic shot having physico-mechanical characteristics substantially close to the material of the metal workpiece being clad.

2. In a method as claimed in claim 1, wherein said pad of metallic shot is enclosed in a container, said container having a top portion of at least one wall thereof subject to maximum impact load at the moment of explosion welding, said wall being made of a pliable material and adapted for an unobstructed discharge of some amount of said shot from said container at the moment of explosion.

3. In a method as claimed in claim 1, in case of cladding metal products in a medium having subzero temperature, further including the step of heating the pad of metallic shot to a temperature enabling the workpiece being clad, when placed on said pad, to have above-zero temperature by the moment of explosion welding, with the result that cladding occurs at a rather good impact strength of the material of the workpiece being clad.

4. In a method as claimed in claim 1, wherein in case of cladding metal products up to 40 mm thick, said pad of metallic shot is enclosed in a container and immersed in a liquid.

5. In a method as claimed in claim 1, wherein said pad of metallic shot is embraced in an air-inflated tire. 

1. IN A METHOD OF CLADDING METAL PRODUCTS, WHEREIN THE WORKPIECE BEING CLAD IS PLACED ON A SUPPORT AND SUBJECTED TO CLADDING BY THE EXPLOSIVE-WELDING TECHINQUE, THE IMPROVEMENT WHICH COMPRISES THE STEPS OF PROVIDING A "PAD" OF METALLIC SHOT WITH WHICH THE WORKPIECE BEING CLAD MAKES A DIRECT PHYSICAL CONTACT SO AS TO BE THE SUPPORT FOR ACCOMMODATING THE WORKPIECE; AND SELECTING THE MATERIAL OF THE METALLIC SHOT HAVING PHYSICO-MECHANICAL CHARACTERISTICS SUBSTANTIALLY CLOSE TO THE MATERIAL OF THE METAL WORKPIECE BEING CLAD.
 2. In a method as claimed in claim 1, wherein said ''''pad'''' of metallic shot is enclosed in a container, said container having a top portion of at least one wall thereof subject to maximum impact load at the moment of explosion welding, said wall being made of a pliable material and adapted for an unobstructed discharge of some amount of said shot from said container at the moment of explosion.
 3. In a method as claimed in claim 1, in case of cladding metal products in a medium having subzero temperature, further including the step of heating the ''''pad'''' of metallic shot to a temperature enabling the workpiece being clad, when placed on said ''''pad,'''' to have above-zero temperature by the moment of explosion welding, with the result that cladding occurs at a rather good impact strength of the material of the workpiece being clad.
 4. In a method as claimed in claim 1, wherein in case of cladding metal products up to 40 mm thick, said ''''pad'''' of metallic shot is enclosed in a container and immersed in a liquid.
 5. In a method as claimed in claim 1, wherein said ''''pad'''' of metallic shot is embraced in an air-inflated tire. 